How can Edge Loops stay aligned when using the Subsurf Modifier?
Set the edge Crease weight (Shift+E or Properties shelf Transform panel Mean Crease):


  Weighted edge creases for subdivision surfaces allows you to change the way Subsurf subdivides the geometry to give the edges a smooth or sharp appearance.
  
  The crease weight of selected edges can be changed using Transform Properties (N) and change the Median Transform slider. A higher value makes the edge “stronger” and more resistant to subsurf. Another way to remember it is that the weight refers to the edge’s sharpness. Edges with a higher weight will be deformed less by subsurf. Recall that the subsurfed shape is a product of all intersecting edges, so to make the edges of an area sharper, you have to increase the weight of all the surrounding edges.